1. Technical Field
The present disclosure relates generally to the production of chloral by chlorination of acetaldehyde, and more particularly to apparatus and methods for converting acetaldehyde to chloral, via liquid phase chlorination, in a high shear process. More specifically, the disclosure relates to the reduction of mass transfer limitations in apparatus and methods for converting acetaldehyde to chloral.
2. Background of the Invention
Chloral, CCl3CH═O, also known as trichloroacetaldehyde or trichloroethanal is an organic halide discovered in 1832 by Justus von Liebig. Chloral in pure form is a colorless oily liquid soluble in alcohol and ether. Chloral reacts with water to form chloral hydrate which has medicinal properties as a potent sedative. Historically, chloral was reacted with chlorobenzene in the presence of sulfuric acid catalyst to form DDT in the pesticide industry.
Chloral is typically produced by the chlorination of ethanol or aldehyde. Specifically during the chlorination of aldehydes, the raw materials acetaldehyde or paraldehyde may be used. Due to loss of ethanol via formation of ethyl chloride and ethyl acid sulfate as well as environmental and waste disposal problems associated with production of these materials, the ethanol process has been largely replaced by aldehyde chlorination. Acetaldehyde chlorination is carried out via the reaction:CH3CHO+3Cl2→CCl3CHO+3HCl  (1)Chloral is an unstable compound, making it highly reactive such that it may combine with many chemical substances, including itself, or decompose.
Conventionally, the commercial practice of manufacturing chloral from acetaldehyde involves adding water to the material undergoing chlorination to inhibit decomposition of dichloroacetaldehyde and chloral by their reactions with chlorine. Chloroform and carbon tetrachloride result from decomposition. Presumably the decomposition reactions are inhibited by formation of the hydrates.
The hydrates are much more stable and therefore production of crude chloral containing only trace amounts of dichloroacetaldehyde, without significant chloroform and carbon tetrachloride co-production, can be accomplished. The chlorination reaction in addition generates significant amounts of byproduct hydrogen chloride gas (HCl) some of which tends to be absorbed by the wet crude chloral. To produce the purified chloral from the wet crude product, water and HCl must be removed. Many patents discuss methods of wet crude chloral purification, including U.S. Pat. Nos. 4,513,152; 774,151; 2,443,183; 2,478,152; 2,478,741; 2,768,173; 955,589; and 661,092.
Accordingly, there is a need in the industry for improved methods of producing chloral from acetaldehyde and chlorine whereby production rates are increased, unwanted reactions are reduced, and milder reaction conditions, such as lower temperature and pressure, are commercially feasible.